Currently, the manufacturing process of the Complementary Metal Oxide Semiconductor Field Effect Transistor (CMOSFET) is researched approximately in two directions, i.e., a gate-first process and a gate-last process.
The gate-last process is widely applied in the advanced integrated circuit manufacturing process. The gate-last process generally includes firstly forming a pseudo gate and a source-drain region, and then removing the pseudo gate and re-filling a gate trench with an alternative gate of a high-k metal gate stack. As the gate is formed after a source and a drain are formed, the gate will not sustain a high annealing temperature in the process. Therefore, the material of the gate layer is more widely selected and the intrinsic properties of the material can be better embodied.
Conventional approaches such as CVD, PVD etc. are typically used to prepare metal such as Al, Mo etc. to form a metal filling layer of the alternative gate. However, the step coverage thereof is poor, and an ultrathin metal layer of a small-sized device is difficult to be controlled through a subsequent CMP process. Thereby, quality of the prepared metal layer fails to meet process requirements of a device in a size less than 40 nm.
An Atomic Layer Deposition (ALD) process is surface reaction-limited based on chemical absorption, which can provide intrinsic single-layer deposition, and achieve 100% step coverage in a gap with a high depth-to-width ratio. Currently, the gate trench is generally filled with metal W through the ALD process in the gate-last process, to form top-layer metal of the alternative gate. In this way, a high-quality metal layer with good step coverage and gap filling capability is provided, thereby meeting requirements of the device in a size of less than 40 nm.
However, when W is prepared through the ALD, B2H6 and WF6 are typically used as precursors. In this case, B will diffuse into the metal gate and a gate dielectric layer with high-k material, which will influence the performance and reliability of the device.